1. Field of Invention
The invention concerns a stamping roller intended for a stamping apparatus, which has a central carrier roller and stamping punch portions which are spaced from each other in the peripheral direction, wherein fixed to the carrier roller is at least one punch ring whose two axially mutually spaced edge portions are designed with spacer rings for the defined contact of at least one associated backing roller, and the at least one punch ring is designed with the stamping punch portions between the two associated spacer rings.
2. Description of the Prior Art
A stamping roller, or embossing roller, is known from WO 94/13487 A1, in which a specific stamping roller is required for different substrates to be stamped or embossed, according to the way in which the substrates are respectively divided up into respective pieces or portions. That means that a known stamping roller of that kind is only suitable for stamping large numbers of items because such stamping rollers are expensive and so-to-speak exhibit no flexibility. In addition, when such a known stamping roller is of large dimensions, minimal deviations from the ideal cylindrical shape, as can occur for example due to temperature influences, can give rise to considerable quality problems in the stamping operation, that is to say in the respective operation for transferring decoration from the stamping foil onto the substrate, because the pressure or backing rollers which press against the stamping roller can provide for only limited compensation in respect of such deviations from the ideal cylindrical shape for the stamping roller, or tolerance compensation.
A stamping roller intended for a stamping apparatus is known from German patent specification No. 233 239, which stamping roller has a central carrier roller and stamping punch portions which are spaced from each other in the peripheral direction, wherein a number of punch rings are fixed to the carrier roller in closely adjacent relationship. The punch rings are arranged between two lateral spacer rings. Those two lateral spacer rings serve therein not for defined contact of an associated backing roller, but for passing through and securing fixing bars for holding together the punch rings which are arranged in closely adjacent relationship.
DE 27 53 296 C2 describes a slur ring arrangement for producing a defined interaxial spacing between two printing mechanism cylinders of a rotary printing mechanism with two slur rings mounted at a respective end of each of the two printing mechanism cylinders and which rotate with the printing mechanism cylinders and which can roll against each other in a prestressed condition and with continuous contact with each other, at least one thereof being fixed with its central bore on the shaft of the associated printing mechanism cylinder. To prevent slur ring wear it is proposed therein that in the case of the slur ring which is fixed on the shaft of the printing mechanism cylinder, the support surface at the shaft of the printing mechanism cylinder is convex and the support surface in the central bore of the slur ring is correspondingly concavely curved.
DE 85 18 933 U1 discloses a stamping roller with a heatable roller core and a roller shell which is supported thereon and which is engraved on its peripheral surface, wherein the roller core, at least in the region of its support with the roller shell, comprises a material with a higher coefficient of thermal expansion than the roller shell.
The object of the present invention is that of providing a stamping roller of the kind set forth in the opening part of this specification, in which a variable arrangement of the stamping punch portions is possible as desired and in which tolerances or possible deviations from the ideal cylindrical shape of the stamping roller and truth-of-rotation thereof can be compensated, using simple means.
In a stamping roller of the kind set forth in the opening part of this specification, in accordance with the invention, that object is attained in that the/each punch ring is matched to the carrier roller in respect of dimensions and material in such a way that the/each punch ring is displaceable on the carrier roller at ambient temperature and at elevated stamping or operating temperature of the stamping roller thermal expansion fixes the/each punch ring on the carrier roller, that the/each punch ring has a heat-insulation portion between the two lateral spacer rings and between adjacent stamping punch portions, and that cover means laterally adjoin the/each punch ring.
In that arrangement, the stamping punch portions are desirably disposed equidistantly in the peripheral direction of the punch ring. A punch ring can be fixed to the central carrier roller but preferably a plurality of punch rings are fixed to the central carrier roller. By virtue of the fact that the stamping punch portions are provided on punch rings, it is possible for a suitable number of punch rings to be arranged as desired on the central carrier roller. In that respect, the axial spacing between the adjacent punch rings can be easily adjusted as desired. The selection of a suitable punch ring also makes it possible for example to select as desired the pitch or the mutual spacing of the stamping punch portions in the peripheral direction of the stamping roller. Because the respective pressure or backing roller bears in a defined manner against the two lateral spacer rings between which the stamping punch portions are disposed, that gives the advantage that tolerances in the stamping roller or deviations in the stamping roller from an exact cylindrical shape and thus deviations from precise rotational truth of the stamping roller can be easily compensated. It will be appreciated that it is also possible for not just one pressure or backing roller to bear against the corresponding punch ring, but a number of pressure or backing rollers, similarly to a design configuration of a stamping apparatus as is disclosed in DE 32 10 551 C2.
At normal abient temperature there is a sliding or push fit tolerance between the respective punch ring and the central carrier roller, so that the respective punch ring is displaceable as desired in the axial direction of the central carrier roller. The choice of material for the punch ring and the central carrier roller is such that, at the elevated operating or stamping temperature of the stamping roller, the central carrier roller expands to a greater degree than the/each punch ring, so that there is a press fit between the central carrier roller and the/each punch ring at the stamping or operating temperature of the stamping roller, whereby the/each punch ring is fixed on the central carrier roller.
Desirably, the/each punch ring is provided with a heating device. The heating device may be an electrical heating device. By means of such a heating device, it is possible to provide for accurate regulation of the temperature at the stamping punch portions of the respective punch ring and in particular precise regulation of the temperature at the front or punching surfaces of the individual stamping punch portions. For the purposes of accurate temperature regulation of the individual stamping punch portions of the/each punch ring, the respective punch ring is desirably provided with temperature-measuring sensors connected to a regulating device which suitably acts on said heating device.
Thermal separation between the stamping punch portions or the front or stamping surfaces thereof can be achieved by the/each punch ring having a heat-insulation portion between the two lateral spacer rings and between the adjacent stamping punch portions. Those heat-insulation portions advantageously have an outside surface which corresponds to the outside surface of the stamping roller. That affords the advantage that the substrate which is to be stamped and the stamping foil which is introduced simultaneously with the substrate between the stamping roller and the at least one associated pressure or backing roller cannot suffer from any undesired folding into the intermediate spaces between adjacent stamping punch portions, which folding would adversely affect the quality of the stamping. The above-mentioned heat-insulation portions have insulating properties such that the surface temperature of the heat-insulation portions does not exert any effect, that is to say influence, on the stamping foil, so that the heat-insulation portions do not give rise to any undesired preliminary activation of the adhesive layer and/or stretching of the carrier of the stamping foil.
While, in the case of a smooth stamping roller as is disclosed for example in above-mentioned DE 32 10 551 C2, the pressure or backing rollers continuously and uniformly roll against the cylindrical peripheral surface, the rolling movement is correspondingly discontinuous in the case of a stamping roller with spaced-apart, individual stamping punch portions. In other words, at the pressures required for carrying out the stamping operation, the backing or pressure rollers can be moved into the intermediate spaces between adjacent stamping punch portions. The heat-insulation portions disposed between adjacent stamping punch portions are not suitable for applying the necessary counteracting forces; more specifically, due to the material used, they yield or deflect slightly. Serious problems can arise, in particular in the event of so-called distortion of the stamping roller, as often cannot be reliably excluded in consideration of the temperatures employed. It is here that the present invention, using simple means, provides a reliable remedy by virtue of the fact that disposed laterally beside the spaced-apart stamping punch portions are the two spacer rings against which the at least one associated pressure or backing roller of the stamping apparatus presses. When dealing with sensitive substrates to be stamped and/or when using high line pressures between the stamping roller and the at least one pressure or backing roller, the spacer rings can leave behind on the stamped substrate clearly marked impressions which can then limit the capacity for overprinting. In order to remedy that disadvantage, the two spacer rings of the/each punch ring in the stamping roller according to the invention can be provided with chamfer surfaces. Designing the respective pair of spacer rings with such chamfer surfaces affords the advantage that overprintability is not restricted.